The operation of our magnetometer is sketched in Fig. REF .
The circularly-polarized pump laser beam (\(\lambda \sim \) 894 nm) is resonant with the \(4{\rightarrow }3\)  hyperfine component of the \(6S_{1/2}{\rightarrow }6P_{1/2}\)  (\(D_1\) ) atomic transition spin-polarizes the cesium atoms by optical pumping, see Chapter 4 in [1]}.
The probe laser beam is linearly-polarized and its polarization is analyzed by a balanced polarimeter.
The system is operated in a magnetically unshielded environment, in which the local laboratory field is compensated and an offset field \(B_0\)  of \(\approx \) 27 \(\mu \) T (corresponding to a Larmor frequency of \(\approx \) 100 kHz) along \(x\)  is applied to the atoms.
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